1. Field of the Invention
The present invention relates to a transparent electroconductive material which comprises a substrate of a synthetic resin and a transparent electroconductive film formed thereon, wherein an excellent adhesion exists between the transparent electroconductive film and the substrate, and a process for the preparation of this transparent electroconductive material.
2. Description of the Prior Art
A transparent electroconductive substrate is widely used as an electrode of a liquid crystal display device or electroluminescence emitter, a transparent face heat generator, a touch panel switch, an electrostatic screening material, an antistatic material and the like.
Conventional transparent electroconductive substrates are composed mainly of glass, and recently, a transparent electroconductive substrate comprising a substrate composed of a heat-resistant polymer film such as a polyester or polyimide film and a film of a metal such as gold, palladium or aluminum or a indium-tin oxide semiconductor film coated on the substrate, has been proposed.
An electroconductive substrate composed of glass has an excellent transparency and electroconductivity but exhibits poor flexibility, impact resistance and processability, and there is little reduction in the weight, which is important for practical utilization.
An electroconductive material having a plastic substrate exhibits excellent processability, impact resistance, and light weight characteristics, but the transparency of the substrate per se is lower than that of glass, and hence, a thick material such as a plate can not be practically used in fields where a high transparency is required. More specifically, a practically applicable substrate of this type is limited to a filmy product having a thickness of up to several hundred microns. For example, when polyethylene terephthalate is used as the substrate, if the quantity of deformation by an external stress is about 5 to about 30%, a large change of about 50.times.10.sup.-3 to about 100.times.10.sup.-3 is caused in the optical birefringence, resulting in a reduction of the transmittance and in optical distortion. Therefore, the thickness must be reduced to avoid these disadvantages. Furthermore, since the optical distortion is large, as mentioned above, where the substrate is used as an electrode of a liquid crystal display device or the like, even if the film thickness is reduced, a uniform image cannot be obtained.
Moreover, the adhesion of the plastic substrate to a transparent electroconductive film which is composed of an inorganic material is poor. Methods for improving the adhesion between the transparent electroconductive film and the organic substrate have been proposed in Japanese Unexamined Patent Publications No. 55-36280 and No. 56-10450. But, even according to these methods, it is impossible to obtain a transparent electroconductive substrate having a large substrate thickness, a small optical distortion, and an excellent transparency.